Sepsis is a serious medical condition caused by the body's response to an infection. The source of the infection can be any of a number of places throughout the body. Bacterial infections are the most common cause of sepsis, but sepsis can also be caused by fungal, parasitic, or viral infections. Toxins produced by an untreated or inadequately treated infection circulate in the bloodstream causing damage, for example, to the brain, heart, lungs, kidneys and liver. Severe sepsis can result in septic shock, a medical emergency in which the organs and tissues of the body are not receiving an adequate flow of blood.